In recent years, the presence of carbon dioxide in the atmosphere has become an increasing ecological concern. While the carbon dioxide in the atmosphere can have many sources, one source is the release of carbon dioxide into the air as leakage from wells penetrating subterranean carbon dioxide-containing formations.
Such formations may contain carbon dioxide as a result of naturally-occurring in situ carbon dioxide, from use of the well as a carbon dioxide injection/disposal well, from use of the well as either an injection or a production well in a carbon dioxide enhanced oil recovery process, and the like. There are a variety of reasons why subterranean formations containing carbon dioxide are desirably isolated so that the carbon dioxide does not flow into the atmosphere. The most commonly used technique for isolating such formations is plugging the wells penetrating the formation containing carbon dioxide. This is most commonly accomplished by cementing the wells shut.
Of continuing concern is whether the cement plug, or other plugging material, has fully plugged the well and whether it continues to block the carbon dioxide from flowing upwardly through the well into the atmosphere. Should leaks occur, the source of leaks into the atmosphere can be through or around the cement plugging, which cements the casing in place in the wellbore, or through or around the cement plugging the inside of the casing, which is typically used to case the well from the earth's surface to or through the carbon dioxide-bearing formation.
Various techniques have been used in the past for carbon dioxide measurement. These techniques include near infra red or other light absorption techniques and the like for the detection of carbon dioxide in flowing gas streams. However, such techniques are not effective for the detection of very minute quantities of carbon dioxide released on a continuing basis. Accordingly, an improved method for detecting carbon dioxide leakage from plugged wells has long been sought.